Let's see 4L is about .8 gallons, which is much too small. If you are going to keep them in that you need to do a 100% water change every day. Ammonia is constantly excreted from the gills. In 4L it builds up very fast and after 7-10 it can become very toxic. Doing a water change will stop the ammonia from building. I would get 2.5 gallon tanks or 5 gallons (which you can divide). Most kits come with a heater, filter, hood, and light. I'm not sure how to treart ammonia burns, you'll have to go to disease forum. And for you CT who's bloated just fast for a few days until there is no bulge. How much do you feed?